This invention relates to a system and method including a video camera and video display devices and associated apparatus for instantaneously viewing, transmitting and reproducing the images recorded on x-ray film; and more particularly to a video camera, for use in such a system, with automatic control to correct the video signal in relation to the overall level of light projected through the x-ray film.
An object of this invention is to provide an improved system and method for viewing x-ray film by means of video monitors.
Another object of this invention is to provide an improved system and method, including a novel video camera and controls, for viewing back lighted x-ray film.
A further object of this invention is to provide a novel video camera with control systems for automatically adjusting the video camera output to the levels of light projected to the camera.
Still another object of this invention is to provide a novel video camera with automatic control means for adjusting and maintaining the proper ratio of video signal amplitude and blanking pedestal amplitude, for the purpose of maintaining proper brightness and contrast levels of the picture quality in relation to the variation in light transmitted to the camera.
Another object of this invention is to provide a novel video camera including circuitry for automatically controlling the voltage level of the target electrode in relation to the variation in light transmitted to the camera.
An important overall object of this invention is to provide a system and method for video viewing of x-ray film with acceptable resolution for all investigative purposes whether medical, industrial or other; and to produce a video signal enabling high quality tape recording, and for later reproduction of a video image with acceptable resolution.
Still another object of this invention is to provide a system and method for high quality transfer of x-ray images from x-ray film to video tape enabling significant storage and reproduction economies in relation to storage and later display of conventional x-ray film.
Another important object of this invention is to provide a novel video camera having circuitry for reproducing, without distortion or degradation of picture quality, the full range and spectrum of the total gray scale from "reference black" to "peak white", and with full reproduction of each and every minute shade of gray that necessarily appears in viewing x-ray film.
Still another object of this invention is to provide a novel video camera including circuitry which permits the camera to view, without distortion, direct incoming light rays from the subject film, and still reproduce and delineate the remainder of contrast and detail of an x-ray film. A related object is to produce this result with automatic circuitry and without the need for any "operating" control adjustments.
These objects are accomplished in a video camera which includes a pickup tube with electron beam generating means and a target plate, means for vertically and horizontally deflecting the electron beam, means for generating blanking and synchronizing signals for blanking the electron beam and controlling the deflection means in synchronism therewith, amplifying means including a plurality of stages connected to the output of the target plate for amplifying the composite video signal produced thereby, and clamping circuit means for coupling the blanking signal generating means and the amplifying means. The amplified composite video signal is fed to an amplification correction circuit which includes means for removing the blanking component from the composite video signal, means for rectifying the remaining video signal component to produce a varying DC reference voltage signal proportional to the video signal component, and means for feeding this DC reference voltage signal as an amplification correction signal to the output bias voltage circuit for one of the video amplifier stages for varying the gain of that one amplifier stage. The amplified composite video signal is also fed to a pedestal amplitude correction circuit which includes means for restoring the DC component of said composite video signal, RC network means for producing an output signal corresponding to the average value of the restored DC signal as a pedestal level correction signal, and feeding that correction signal to the clamping circuit for correcting the pedestal level at the video amplifier. A target voltage correction circuit includes a series DC bias voltage circuit connecting the target plate with a regulated DC voltage source, the series circuit including an ultra-high resistor, a variable resistor defining a voltage limiter, and a load resistor. The voltage limiter enables the setting of an optimum level of target voltage which will be automatically adjusted above and below the optimum value by the flow of target plate current.
The novel features and the advantages of the invention, as well as additional objects thereof, will be understood more fully from the following description when read in connection with the accompanying drawings.